WebSocket is known as a Web standard communications protocol that keeps (maintains) an established communication connection and achieves bidirectional low-delay communication. Remote control system technologies using both this WebSocket and a polling system have been proposed. There is a known problem with WebSocket communication in that an interposed relay device (e.g., broadband router) disconnects a communication connection when a no-communication state continues for a certain amount of time. In the above-mentioned remote control system technologies, there is no disclosed method that avoids or solves this problem, specifically, a mechanism that can keep a communication connection for a long time. In general, a mechanism to keep a communication connection is known, where keep-alive packets are transmitted at a short cycle (e.g., one minute) to keep a communication connection.
In a scheme in which keep-alive packets are transmitted at a short cycle, in the case where it is required to accommodate a large number of clients, a communication cost or a CPU load due to the transmission of keep-alive packets becomes considerable. Especially, many of cloud computing services, which have been in widespread use nowadays, adopt usage-based rates on their communications, and thus increasing traffic has direct influence on an operational cost, which is required to be reduced as much as possible.